Click for Coverage
Due to the EU’s Global Data Protection Regulation, our website is currently unavailable to visitors from most European countries. We apologize for this inconvenience and encourage you to visit for the latest on new cars, car reviews and news, concept cars and auto show coverage, awards and much more.MOTORTREND.COM
  • JP Magazine
  • Dirt Sports + Off-Road
  • 4-Wheel & Off-Road
  • Four Wheeler

Optima Group 31 Battery

Posted in Product Reviews on February 1, 2005
Share this

Having used a prototype deep-cycle Optima in our trail beater since early 1996 or so, that battery has certainly served us well. While it still performs quite well when winching, and even puts up with running the electric cooler 24 hours a day, we were thinking about going to dual batteries. That was until we realized the potential benefits of using a single, larger battery instead.

There are indeed times when bigger can be better, and the newest Optima is one such product. Group 31 batteries are pretty large, used mostly in industrial applications, earthmovers, trucks and other big stuff. Compared to a regular Group 34 Optima, the 31 is 45 percent bigger in volume and 37 percent in weight, but a heavier battery is generally a better battery-and Optimas are darn good to start with (pun intended). Consider the numbers in the chart, which are on Optima's and several other Web sites, and you may see why a single 31 can be a good alternative to dual 34s.

Apparently, by going with a Group 31 Optima, we did need room for a 21 3/16-inch-longer and 1 9/16-inch-taller battery, but the footprint is only 22 percent bigger. In return, this got us 30 percent more starting and/or winching capacity-at freezing temperature. Batteries don't like cold anymore than we do, and operate far better at room temperature, so anything over 32 degrees will make the battery work better yet. Also, if it's that cold, it is probably a moot point that our Engle cooler could run for over 30 hours (on warm days) before the Group 31 Optima was sucked down to 10.5 Volts (100 percent discharge), and then it'd probably still start our engine.

Optima's newest battery is the Group 31, a larger and more potent version of the tried-and-true spiral "6-pack" technology. With a footprint 22 percent larger than a regular Optima battery, it may not fit all applications, but where it does, there are large gains in performance to be had. For example, 30 percent more power for winching than a Group 34 offers. Also, a single Group 31 can be a viable alternative to dual 34s, but with fewer connections to create resistance and potential trouble, and for a lot less money.

Optima Battery Comparison Chart
  D34/78 D31A/D31T % increase
Cold Cranking Amps @ 0 deg. F 750 {{{900}}} 20
Cranking Amps @ 32 deg. F 870 1,125 30
Reserve Capacity 120 155 30
Capacity (C/20 rate) 55 75 35
Internal Resistance (ohms)* .0028 .0025  
Length (in.) 10 121 3/16 28
Width (in.) 6 7/8 6 1/2 -6
Height (in.) 71 3/16 9 3/8 20
Weight (lb.) 43.5 59.8 37
Price ($) 147.50 171.25 16
*Here, lower is better

Connect With Us

Newsletter Sign Up

Subscribe to the Magazine

Browse Articles By Vehicle

See Results